In a radio communication device the transmitting/receiving circuits are coupled to the feed point of a radiator means via a feed line. Normally, the transmitting/receiving circuits have a nominal impedance of 50+j0 ohm. If the impedance of the radiator feed point differs substantially from that of the transmitting/receiving circuits, an impedance matching means is required for matching the impedance of the radiator to the impedance of transmitting/receiving circuits.
The radiator and the impedance matching means may then be interconnected by a second feed line or similar having a given length. This feed line is influenced electromagnetically by different conductive or dielectric bodies in its surroundings, for example a support on which the radio device is resting, the hand and head of an operator, or the chassis of the radio device or conductive parts thereof. Especially when the radiator feed point impedance is high, the length of the second feed line is significant to the environmental influence on the antenna performance. The higher the impedance of the feed point and the longer the second feed line, the higher the sensitivity to environmental variations.
A radiator of quarter-wave type may not require an impedance matching means to be connected to 50 ohm circuitry. Sometimes, a quarter-wave radiator is preferred since it allows the antenna means to be relatively short and non-obstructive. However, a drawback of quarter-wave radiators, for example in cellular telephones, is that currents are inevitably generated on the chassis of the telephone. The antenna performance is then sensitive to influence by, for example, the operator holding the telephone or pressing it to his ear.
Also, from another point of view, it is desirable to use a radiator with relatively high impedance, for example a half-wave type radiator or similar. Generally, a half-wave type radiator provides a higher efficiency and a greater overall length resulting in less screening. Particularly, on a small size cellular telephone, screening by the operator's head is a problem with regard to operating range.
In WO-A1-97/42680 it is disclosed an antenna device for a portable radio communication device, where a radiating first element is substantially directly connected to the impedance matching means.
WO-A1-98/07208 discloses an integrated matched antenna assembly, having a matching circuit including an inductor formed on a substrate. A capacitive element having two conductors in spaced relation to each other is connected to the inductor by one of the conductors being arranged parallel to the inductor. This arrangement requires several conductive layers and at least two substrates. Further, wires can be used for connecting components of the matching device.
JP-A-6152221 discloses an antenna for mobile radio equipment. The antenna is connected to one terminal of a meandering transmission line whereof the other terminal is connected to ground, and a feed point is arranged on the transmission line. These arrangements are provided inside the telephone and require a feed line to the antenna feed portion, and discrete capacitive components.
WO-A1-96/37007 discloses an antenna apparatus, wherein a radiator is connected to one end of a spiral conductor of which the other end is connected to a transceiver. A drawback with this apparatus is that the spiral has one central and one peripheral connection. Further, a feed line is provided between a connecting portion of the spiral and the antenna.
Some general problems with matching devices or circuits are that they are space demanding, complicated to assemble and complicated to mount. Generally, the arrangements of the connections also cause problems. This is especially apparent when the matching device is located inside a radiotelephone housing, includes discrete components, or is not or can not be formed into a space optimising shape.